This invention relates to a device for forming fibre balls of elongated fibres carried in an air flow. Particularly this relates to such a device having a stator chamber with a circular cross section in which there is arranged coaxially with it a rotor which also has a circular cross section and which is rotatable around its axis and has on its periphery a plurality of circumferentially spread radial blades at a short distance from the stator""s inner wall, whereby fibres carried by the air flow are directed from the input opening at one end of the stator chamber into said intermediate space and removed through an output opening at the opposite end of the rotor chamber in order to separate fibre balls from the air flow.
Fibres are generally used as stuffing in upholstery. In order to make upholstery as spongy as possible the fibres are often made into spongy fibre balls with a rather smooth surface so that the balls are resilient and also able to move in relation to each other, in order to make the stuffing as loose as possible. There are previously known devices for forming balls of opened fibres carried in an air flow. Due to the surface friction the opened fibres carried in the air flow are attached to each other forming floccules of different sizes and forms. These floccules are not as such suitable for a stuffing material as there are fibre ends protruding from them which easily are attached to fibres protruding from other floccules. Therefore the floccules are preferably formed into balls.
Such ball forming devices are known for instance from the U.S. Pat. Nos. 4,747,550 and 5,429,783. In these previously known devices the opened fibres carried in the air flow are formed into balls in the intermediate space formed by the inner wall of a cylindrical stator chamber and the periphery of a rotor arranged coaxially within the stator. A plurality of transverse discs are arranged spaced from each other on the rotor shaft, whereby at the outer edges of the discs there are at mutual peripheral distances fastened radial blades having outer edges which end at a short distance from the inner wall of the rotor chamber. Air and fibres are supplied to the lower part of the rotor chamber and blown from there further upwards, whereby the fibres are formed into balls in the intermediate space formed by the outer edges of the blades and the inner wall of the stator chamber when they are carried upwards in this intermediate space. Then the fibre balls are sucked from the upper part of the stator chamber into a cyclone separator where the fibre balls are separated from the conveying air.
The gap between the outer edge of the blades and the internal wall of the stator chamber is in these devices generally 4 mm, but it can be made larger depending on the length and other characteristics of the fibres to be treated. However, in these devices it is a cumbersome and time-consuming task to alter the gap. In order to adjust the blades the rotor chamber must be opened and the rotor removed from the rotor chamber, after which the fastening of each blade must be loosened, adjusted and refastened. The blades are situated in many planes, and each plane contains many blades, and thus it is obvious that the blade adjustment operation is quite tricky and takes a long time.
The object of the present invention is to remove the above-mentioned disadvantage and to provide a device of the type presented in the preamble of claim 1 for forming fibre balls of elongated fibres carried in an air flow, whereby the device is novel and original in that the stator chamber and the rotor are substantially conical and that they can be mutually positioned in the axial direction.
With the solution according to the invention the intermediate space between the inner wall of the stator chamber and the blades of the rotor can be adjusted in a rapid and simple manner so that is suitable for each fibre quality, without having to open the stator chamber in order to remove the rotor from it, and without having to loosen, adjust and refasten the blades and without having to rearrange the rotor into the stator chamber and close the stator chamber. Thanks to the conical shape of the combination of stator chamber and rotor said intermediate space changes when the stator chamber and/or rotor is moved in the axial direction. The intermediate space changes the more the larger the coning angle is, and the more the greater the axial movement is.
In a preferred embodiment of the invention the blades are located on a plurality of axial planes, so that the blades on one plane are peripherally displaced in relation to the blades in the adjacent plane or planes. The angle of displacement is preferably 3 to 5 degrees, for instance 4 degrees in relation to the blades on the next plane.
Further, the blades on different planes are preferably separated from each other by circular plates, which are transverse in relation to the rotor shaft and of which the top plate has a radius which is substantially smaller than the radial length of the rotors below it. These solutions present a particularly advantageous and effective ball forming of elongated fibres. The blades are generally at a mutual distance of 20 degrees in the direction of the rotor periphery, whereby the blades are advantageously on 4 to 6 planes, for instance on 5 planes.
In a particularly preferred embodiment of the invention the combination of stator chamber and rotor is in a substantially vertical position and widens downwards, whereby the input opening is at the upper end of the stator chamber. Thanks to the conical shape of the combination of stator chamber and rotor there is formed a so called tornado effect in the intermediate space between the stator chamber and the rotor when the gas flow accelerates as it propagates in a spiral manner towards the wider end of the conical combination of stator chamber and rotor. The velocity of the gas flow increases as the peripheral distance is increased but at the same time the time used for one revolution is kept substantially the same. As the velocity of the gas flow increases its pressure will correspondingly decrease, there is in other words created a pressure difference between the ends of the combination of stator chamber and rotor, and this pressure difference tends to force the flow combination against that end of the combination having the larger diameter. When the combination of the stator chamber and the rotor is in a substantially vertical position and widens downwards the above mentioned effect is assisted by the gravity, and thus it is effectively secured that the small fibre balls move towards the output opening at the lower end of the combination.
It has been found that the forming of balls is particularly effective when a part of the blade is bevelled at the outer edge, on the trailing side as seen in the rotation direction, whereby the bevelling angle of the blades is advantageously about 5 to 45 degrees.
Further the forming of balls can be made more effective by means of heating elements in the sheath of the stator chamber, preferably with heating resistors covering the sheath, and by means of a shelf extending around the inner wall of the lower end of the sheath.
Preferably there is further at least one collecting funnel between the output opening and the lower end of the stator chamber for receiving the fibre balls. The funnel is preferably connected to a negative pressure source for removing the fibre balls from the funnel and then for separating them from the carrying air in a manner known per se.
Further there can be a perforated separating chamber between the input opening and the stator chamber in order to remove excessive air from the fibre containing air flow before it is supplied to said intermediate space.
Advantageously the rotor is axially positioned in relation to the stator chamber so that the intermediate space is 4 to 10 mm. Then the coning angle of the combination of the stator chamber and rotor is preferably selected such that an axial displacement of 10 mm between the rotor and the stator chamber corresponds to a change in the intermediate space of about 0.1 to 1.5 mm, for instance 1 mm.
Further the speed of rotation of the rotor is advantageously controlled in a stepless manner.
A device according to the invention is designed so that it can be rapidly and easily adjusted to be suitable for fibres of very different lengths and qualities.
In order to increase the retention time it is possible to connect a plurality of inventive devices in series, and preferably so that the rotational speed of each device can be individually controlled.